This invention relates to techniques for processing video images, and is more particularly concerned with techniques for capturing, storing, enhancing and displaying high resolution video images, especially fluoroscopic or other radiographic images.
The field of digital video radiography has recently received increased attention as a clinical diagnostic procedure, particularly for its advantages over traditional silver-halide film techniques. New radiographic techniques such as digital subtractive angiography (DSA) and digital computerized fluoroscopy have found increasing utility among many health care practitioners because of the capability of producing enhanced images in which diseased or injured tissues can be strongly highlighted.
One example of a computerized digital video fluoroscopic imaging arrangement is set forth in U.S. Pat. No. 4,868,651, granted Sep. 19, 1989, to T.J. Chou et al. In that arrangement the images were industry standard 256 line flames, and produced a matrix or tableau of 256.times.256 pixels.
Recently, because of a desire for increased resolution and detail, the introduction of high resolution video imaging technology now makes it possible to produce radiographic images of extreme resolution, with a line density of 2048 lines per frame, and 2048 by 2048 (or 2K by 2K) pixels per frame.
However, to date it has not been possible for an imaging computer to acquire, store and display a series of high resolution (2K by 2K) images except at an unacceptably low frame rate. Some technological obstacles had earlier precluded high resolution 2K by 2K imaging, but recent advances, particularly in semiconductors and new camera developments, have made high resolution imaging more promising. However, because of the very high density of the images, and the amount of data to be processed and transferred from place to place in the image processing equipment, multiple image acquisition and processing has not been achieved for high resolution images.
Recent advances in semiconductors include the introduction of various CMOS components capable of 40 MHz operation, or faster, such as 10-bit 40-megasample A/D converters and 40 MHz processors. Four-megapixel frame storage is now achievable on a 4 megabit dual-ported video random access memory (VRAM).
Recently a high resolution camera has been introduced, with 2000 line resolution and high signal-to-noise ratio. This new camera employing a Plumbicon XQ5002 imager tube can reproduce an image with four times the number of resolvable elements achieved previously, and when used with an associated low noise amplifier the camera produces its video output signal with a signal to noise ratio of 60 dB.
The camera itself is capable of operating at several combinations of scanning speeds, namely vertical scan rates of 60, 30, 15 or 7.5 Hz, while the horizontal or line rate can be either 31.5 KHz or 15.75 KHz. Additional modes can be established for European standard (e.g. 50 Hz vertical scan rate. ) This provides sixteen modes which can be implemented automatically with various programmable logic devices.
Current designs for radiographic imaging computers have only a limited ability to acquire, enhance, and reproduce high resolution images. Even at the maximum clock rates possible, image data can only be transferred at a rate of a few frames per minute, and the equipment has been unable to acquire and store one set of high resolutions images (for example from a fluoroscope in an examining room) while reproducing a second set of high resolution images (for example on a screen in a radiologist's office).